16 West Coast Regional Plan

Transcription

1 16 West Coast Regional Plan 16.1 Regional overview 16.2 West Coast transmission system 16.3 West Coast demand 16.4 West Coast generation 16.5 West Coast significant maintenance work 16.6 Future West Coast projects summary and transmission configuration 16.7 Changes since the 2012 Annual Planning Report 16.8 West Coast transmission capability 16.9 West Coast bus security Other regional items of interest West Coast generation scenarios, proposals and opportunities 16.1 Regional overview This chapter details the West Coast regional transmission plan. We base this regional plan on an assessment of available data, and welcome feedback to improve its value to all stakeholders. Figure 16-1: West Coast region Construction voltages shown. System as at March

2 The West Coast region includes a mix of significant and growing provincial cities (Dobson, Greymouth, Hokitika), and smaller, lower-growth rural localities. We have assessed the West Coast region s transmission needs over the next 15 years while considering longer-term development opportunities. Specifically, the transmission network needs to be flexible to respond to a range of future service and technology possibilities, taking into consideration: the existing transmission network forecast demand forecast generation equipment replacement based on condition assessment, and possible technological development West Coast transmission system This section highlights the state of the West Coast regional transmission network. The existing transmission network is set out geographically in Figure 16-1 and schematically in Figure Figure 16-2: West Coast transmission schematic NELSON - MARLBOROUGH Stoke Argyle Stoke STC 220 kv Kikiwa Waimangaroa Orowaiti Westport Robertson Street (Buller Electricity) Murchison Inangahua Islington CANTERBURY Atarau Greymouth (Westpower) 33 kv Reefton Dobson 33 kv KEY 220kV CIRCUIT 110kV CIRCUIT 50/66kV CIRCUIT SUBSTATION BUS TRANSFORMER 3 WDG TRANSFORMER Hokitika (Westpower) Kumara (Westpower) STC TEE POINT LOAD CAPACITOR STATCOM Otira Arthur s Pass Castle Hill Coleridge CANTERBURY 271

3 Transmission into the region The West Coast region is connected to the National Grid via a 220/ interconnection at Kikiwa and two circuits from Coleridge. The 220/ interconnection at Kikiwa is effectively operating in parallel with the transformer at Stoke (in the Nelson Marlborough region). The regional generation is lower than the regional demand. Most of the regional load is supplied from remote generation in the Waitaki Valley, with significant load off-take in the South Canterbury and Canterbury regions Transmission within the region The transmission within the region: comprises and transmission circuits, with two 110/ interconnecting transformers at Dobson connects to the rest of the National Grid through two 220/ interconnecting transformers at Kikiwa (one on standby) and two circuits at Coleridge, and derives reactive support from a STATCOM at Kikiwa and capacitor banks at Greymouth and Hokitika. Most of the assets at Robertson Street, Reefton, Atarau, Greymouth, and Hokitika are owned by the associated local lines company (Westpower or Buller Network). The West Coast load is mostly supplied from the northern infeed, with power flowing through the region via the : circuits from Kikiwa to Dobson via Inangahua, and spur from Inangahua to Robertson Street and Westport. Some loads are fed from the south via low capacity circuits from Coleridge, which also provide significant voltage support to the region Longer-term development path The 220/ interconnection at Kikiwa is effectively operating in parallel with the 220/110kV interconnecting transformer at Stoke. In the longer-term, the transformer capacity needs to be increased at Kikiwa and/or Stoke to meet load growth and transmission security requirements to the West Coast region. Possible transmission reinforcement via a third circuit connecting between Kikiwa and Inangahua, additional reactive support, transmission reconfiguration (Kawhaka bonding), and Dobson Greymouth capacity upgrades may be required to support the load growth and transmission security in the West Coast region in the longer-term. Transmission system developments may also be required if there is further generation development. If there is a significant increase in generation, then some of the circuits between Kikiwa and Inangahua may need to be operated at 220 kv West Coast demand The after diversity maximum demand (ADMD) for the West Coast region is forecast to grow on average by 2.3% annually over the next 15 years, from 61 MW in 2013 to 86 MW by This is higher than the national average demand growth of 1.5% annually. 272

4 Figure 16-3 shows a comparison of the 2012 and 2013 APR forecast 15-year maximum demand (after diversity 144 ) for the West Coast region. The forecasts are derived using historical data, and modified to account for customer information, where appropriate. The power factor at each grid exit point is also derived from historical data. See Chapter 4 for more information about demand forecasting. Figure 16-3: West Coast region after diversity maximum demand forecast Table 16-1 lists forecast peak demand (prudent growth) for each grid exit point in the West Coast region for the forecast period, as required for the Grid Reliability Report. Table 16-1: Forecast annual peak demand (MW) at West Coast grid exit points to 2028 Grid exit point Power factor Next 5 years Peak demand (MW) 5-15 years out Arthur s Pass Atarau Castle Hill Dobson Greymouth Hokitika Kikiwa Kumara Murchison Robertson Street Otira Reefton Westport The after diversity maximum demand (ADMD) for the region will be less than the sum of the individual grid exit point peak demands, as it takes into account the fact that the peak demand does not occur simultaneously at all the grid exit points in the region. 273

5 Grid exit point Power factor Next 5 years Peak demand (MW) 5-15 years out The customer AMP advises of new mining loads likely in West Coast generation The West Coast region s generation capacity is 30 MW, which is lower than the local demand and the deficit is imported through the National Grid. Table 16-2 lists the generation forecast for each grid injection point in the West Coast region for the forecast period, as required for the Grid Reliability Report. This includes all known generation stations including those embedded within the relevant local lines company s network (Westpower, Buller Networks, Network Tasman, or Orion). 145 Kumara does not have significant water storage but is expected to supply an average of 4 MW during summer peaks. The new 6 MW Amethyst run of the river hydro project and the Kawatiri Energy Lake Rochfort Hydro scheme are both expected to be operational in Table 16-2: Forecast annual generation capacity (MW) at West Coast grid injection points to 2028 (including existing and committed generation) Grid injection point (location if embedded) Next 5 years Generation capacity (MW) 5-15 years out Dobson (Arnold) Hokitika (Amethyst) Hokitika (McKays Creek) Hokitika (Wahapo- Okarito Forks) Robertson Street (Kawatiri Hydro) Kumara (Kumara and Dillmans) Kumara (Hokitika Diesel) As advised in the Buller Electricity Asset Management Plan Kumara and Dillmans share the same water and are offered into the market as a single 10 MW generator West Coast significant maintenance work Our capital project and maintenance works are integrated to enable system issues to be resolved if possible when assets are replaced or refurbished. Table 16-3 lists the significant maintenance-related work 146 proposed for the West Coast region for the next 15 years that may significantly impact related system issues or connected parties. 145 Only generators with capacity greater than 1 MW are listed. Generation capacity is rounded to the nearest megawatt. 146 This may include replacement of the asset due to its condition assessment. 274

6 Table 16-3: Proposed significant maintenance work Description Arthur s Pass supply transformer expected end-of-life Castle Hill supply transformer expected end-of-life Murchison supply transformer expected end-of-life Kikiwa 220/110/ transformer replacement Westport switchboard replacement Tentative year Related system issues There is no n-1 security at Arthur s Pass. Future investment will be customer-driven. See Section for more information There is no n-1 security at Castle Hill. Future investment will be customer-driven. See Section for more information No n-1 security at Murchison. Future investment will be customer-driven. See Section for more information Upgrading the transformer s capacity and operating in parallel with Kikiwa T2. See Section and No system issues are identified within the forecast period Future West Coast projects summary and transmission configuration Table 16-4 lists projects to be carried out in the West Coast region within the next 15 years. Figure 16-4 shows the possible configuration of West Coast transmission in 2028, with new assets, upgraded assets and assets undergoing significant maintenance within the forecast period. Table 16-4: Projects in the West Coast region up to 2028 Circuit/site Projects Status Arthur s Pass Replace the supply transformer. Proposed Castle Hill Replace the supply transformer. Proposed Dobson Resolve the protection limits on the supply transformers. Resolve the supply transformer s branch limiting component. Install new capacitors. Possible Possible Possible Dobson Greymouth Increase the line thermal capacity. Possible Hokitika Inangahua Murchison Kikiwa Increase the line thermal capacity between Kumara, Hokitika and Otira. Increase the line thermal capacity. Possible Possible Kikiwa Replace Kikiwa T1 with a higher-rated unit. Possible Murchison Replace the supply transformer. Proposed Westport Replace the switchboard. Proposed 275

7 Figure 16-4: Possible West Coast transmission configuration in 2028 NELSON - MARLBOROUGH Stoke Argyle Stoke STC Waimangaroa 220 kv Kikiwa Westport Orowaiti Robertson Street (Buller Electricity) Inangahua Murchison Islington CANTERBURY Atarau Greymouth (Westpower) 33 kv Reefton * Dobson 33 kv KEY Hokitika (Westpower) Kumara (Westpower) Kawhaka NEW ASSETS UPGRADED ASSETS ASSETS SCHEDULED FOR REPLACEMENT MINOR UPGRADE * Otira Arthur s Pass Castle Hill Coleridge CANTERBURY 16.7 Changes since the 2012 Annual Planning Report Table 16-5 lists the specific issues that are either new or no longer relevant within the forecast period when compared to last year's report. Table 16-5: Changes since 2012 s No new issues and no projects have been completed since 2012 Change No change 16.8 West Coast transmission capability Table 16-6 summarises issues involving the West Coast region for the next 15 years. For more information about a particular issue, refer to the listed section number. 276

8 Table 16-6: West Coast region transmission issues Section number Regional Inangahua Murchison Kikiwa transmission capacity Kikiwa interconnecting transformer capacity West Coast low voltage Site by grid exit point Arthur s Pass transmission and supply security Castle Hill transmission and supply security Dobson supply transformer capacity Hokitika transmission capacity Kikiwa supply security Murchison transmission and supply security Otira supply security Bus security Transmission bus security West Coast voltage quality and transmission capacity Inangahua Murchison Kikiwa transmission capacity Project reference: IGH_MCH_KIK-TRAN-EHMT-01 Possible, Base Capex Indicative timing: 2022 Indicative cost band: Thermal upgrade: A Special protection scheme: To be advised There are two parallel circuits between Inangahua and Kikiwa, the: Inangahua Murchison Kikiwa circuit, rated at 56/68 MVA (summer/winter), and Inangahua Kikiwa 2 circuit, rated at 92/101 MVA (summer/winter). An outage of the Inangahua Kikiwa 2 circuit will cause: the parallel Inangahua Murchison Kikiwa circuit to overload from approximately 2022, and low voltage at the West Coast bus from approximately 2026 (see Section for more information). Possible options to resolve the transmission capacity issue include: thermally upgrading the Inangahua Murchison Kikiwa circuit, or a special protection scheme to trip load post-contingency. The preferred option is to thermally upgrade the Inangahua Murchison Kikiwa circuit. However, initial application of the Grid Investment Test indicates that this option has no overall economic benefit. We will investigate other options to resolve this issue closer to the need date. See Section for possible options to resolve the low voltage issue. Easements may be required for some parts of the thermal upgrade project. 277

9 Kikiwa interconnecting transformer capacity Project reference: Indicative timing: Indicative cost band: KIK-POW_TFR-EHMT-01 Possible, Base Capex To be advised B There are two 220/ interconnecting transformers at Kikiwa, T1 and T2 rated at 50 MVA and 150 MVA, respectively. The normal operating arrangement is to have Kikiwa T1 supply the local load only and Kikiwa T2 providing the interconnection with the West Coast region. Kikiwa T2 also operates in parallel with the 150 MVA Stoke T7 interconnecting transformer in the Nelson-Marlborough region due to the network connections between them. The loss of the Stoke interconnecting transformer means the Kikiwa interconnecting transformer supplies both the West Coast and Nelson-Marlborough load, which may overload for: high West Coast and Nelson-Marlborough loads, and low generation in the West Coast and Nelson-Marlborough regions. This issue may be managed operationally with generation from Cobb and Kumara for the forecast period (provided water is available). Transpower will work with the generators to manage this constraint. A possible longer-term option is to replace Kikiwa T1 with a higher-rated transformer that can operate in parallel with Kikiwa T2 and Stoke T West Coast low voltage Project reference: WCST-C_BANKS-DEV-01 Possible, Base Capex Indicative timing: 2027 Indicative cost band: New capacitors: A Special protection scheme: to be advised Low voltage will occur on the transmission system in the region towards the end of the forecast period following an outage of the: Kikiwa T2 interconnecting transformer, or Inangahua Kikiwa 2 circuit. The low voltage issues can be addressed by a local voltage quality agreement if appropriate for the short term. Possible transmission solutions include: installing new capacitors at Dobson a special protection scheme to shed load post contingency, and replacing Kikiwa T1 with a higher-rated transformer, which will address the low voltage issue following a Kikiwa T2 outage (this option also resolves the Kikiwa interconnecting transformer capacity issue described in Section ). We will investigate options closer to the need date. 278

10 Arthur s Pass transmission and supply security This issue is for information only The two circuits supplying Arthur s Pass only have line circuit breakers and protection at Coleridge and Otira. A fault on any section of the Coleridge Castle Hill Arthur s Pass Otira circuits will result in a loss of supply to Arthur s Pass load. Additionally, a single 66/, 3 MVA transformer supplies load at Arthur s Pass, resulting in no n-1 security. Load growth is not forecast to exceed the transformer rating within the forecast period. The lack of n-1 security can be managed operationally. There is a non-contracted on-site spare transformer, allowing possible replacement within 8 to 14 hours following a unit failure (if the spare unit is available). This transformer is also approaching its expected end-of-life within the next five years. We will discuss with Orion options for increasing security and coordinating outages to minimise supply interruptions when replacing this transformer Castle Hill transmission and supply security This issue is for information only The two circuits supplying Castle Hill only have line circuit breakers and protection at Coleridge and Otira. A fault on any section of the Coleridge Castle Hill Arthur s Pass Otira circuits will result in a loss of supply to Castle Hill load. Additionally, a single 66/, 3.75 MVA transformer supplies load at Castle Hill, resulting in no n-1 security. Load growth is not forecast to exceed the transformer rating within the forecast period. The lack of n-1 security can be managed operationally. There is a non-contracted on-site spare transformer, allowing possible replacement within 8 to 14 hours following a unit failure (if the spare unit is available). This transformer is also approaching its expected end-of-life within the next five years. We will discuss with Orion options for increasing security and coordinating outages to minimise supply interruptions when replacing this transformer Dobson supply transformer capacity Project reference: Indicative timing: 2024 Indicative cost band: A Upgrade protection: DOB-POW_TFR-EHMT-01 Upgrade protection: possible, Base Capex Two 66/33 kv transformers supply Dobson s load, providing: a nominal installed capacity of 40 MVA, and 279

11 n-1 capacity of 17/17 MVA 147 (summer/winter). The peak load at Dobson is forecast to exceed the transformers n-1 winter capacity by approximately 1 MW in 2024, increasing to approximately 2 MW in 2028, assuming 3 MW from the embedded generation at Arnold 148 (see Table 16-7). Table 16-7: Dobson supply transformer overload forecast Circuit/Grid exit point Power factor Next 5 years Transformer overload (MW) 5-15 years out Dobson We will use operational measures (Arnold generation) in the short to medium term. Possible longer-term options include resolving the transformers protection and LV cable limits (providing n-1 capacity beyond the forecast period) or increasing the embedded generation. Options will be investigated closer to the need date. Future investment will be customer driven Hokitika transmission capacity Project reference: Indicative timing: 2020 Indicative cost band: C HKK-TRAN-EHMT-01 Possible, Base Capex Two circuits supply the Hokitika grid exit point: Hokitika Kumara rated at 27/32 MVA (summer/winter), and Hokitika Otira rated at 27/32 MVA (summer/winter). An outage of one circuit will cause the other to exceed its thermal capacity from The line from Coleridge to Kumara is predominantly strung with a copper conductor, and therefore cannot be thermally upgraded. Transpower will investigate options closer to the need date. Previous investigations identified a system reconfiguration including: decommissioning the Kumara Otira circuit bonding the circuits between Kumara and Kawhaka 149, and between Otira and Kawhaka, and reconductoring the low-capacity section of the line from Kawhaka to Hokitika, and thermally upgrading the other section. This maintains n-1 security to Hokitika by providing two higher-capacity circuits. 147 The transformers capacity is limited by protection equipment, followed by the LV cable (21 MVA) limits; with these limits resolved, the n-1 capacity will be 22/23 MVA (summer/winter). 148 Arnold is very reliable in producing 3 MW of generation, so its output is considered in the overload forecast. Without Arnold, there is an overload of 1 MW in 2013, increasing to 3 MW in Kawhaka is the point where the lines carrying the Kumara Otira, Otira Hokitika and Hokitika Kumara circuits meet. 280

12 The overloading then shifts to the Dobson Greymouth circuit. Options to address this issue include constraining on generation at Kumara, thermally upgrading the circuit, or load transfer from Greymouth to Dobson. The previous investigations, however, also indicated that the system reconfiguration may be uneconomic. An alternative is to automatically reduce load at Hokitika following a circuit outage, causing a partial loss of supply. We will investigate the appropriate solution for this issue closer to the need date Kikiwa supply security This issue is for information only The Kikiwa load is normally supplied from the tertiary winding of Kikiwa T1 interconnecting transformer, with a backup supply from the T2 interconnecting transformer. Transferring the load between T1 and T2 requires a short interruption to the load. An outage of the switchgear or fault limiting reactor requires a total loss of supply, so there is no n-1 security for these assets. The brief interruption to load and lack of n-1 security can be managed operationally. Future investment will be customer driven Murchison transmission and supply security This issue is for information only The load at Murchison is supplied by: two circuits, which do not have line circuit breakers at Murchison, and a single 110/, 5 MVA transformer. A fault on either circuit or the supply transformer will result in a loss of supply to Murchison. There is a short duration loss of supply whenever the circuits supplying Murchison are switched for maintenance. The lack of n-1 security can be managed operationally. We are installing disconnecting circuit breakers to avoid the loss of supply to Murchison during switching for line maintenance. Additionally, the supply transformer has an expected end-of-life within the forecast period. We will discuss options with Network Tasman for increasing security and coordinating outages to minimise supply interruptions when replacing the Murchison supply transformer Otira supply security This issue is for information only 281

13 Otira is supplied by a single 66/, 2.5 MVA transformer, resulting in no n-1 security. Load growth is not forecast to exceed the transformer rating within the forecast period. The Otira transformer is a three-phase unit. The lack of n-1 security can be managed operationally West Coast bus security The 2013 APR has been expanded to include issues arising from the outage of a single bus section rated at 50 kv and above for the next 15 years. Bus outages disconnect more than one power system component (for example, other circuits, transformers, reactive support or generators). Therefore, bus outages may cause greater issues than a single circuit or transformer outage (although the risk of a bus fault is low, being less common than a circuit or transformer outage) Transmission bus security Table 16-8 lists bus outages that cause voltage issues or a total loss of supply. Generators are included only if a bus outage disconnects the whole generation station or causes a widespread system impact. Supply bus outages, typically and 33 kv, are not listed. Table 16-8: Transmission bus outages Transmission bus outage Arthur s Pass Atarau Castle Hill Loss of supply Arthur s Pass Atarau Castle Hill Generation disconnection Transmission issue Further information Coleridge Arthur s Pass See note 1 Dobson Castle Hill See note 1 Dobson Kikiwa West Coast load Kikiwa 220 kv Inangahua Murchison Kikiwa West Coast load Robertson Street West Coast load Westport Murchison Otira Arthur s Pass See note 1 Castle Hill See note 1 Otira 1. There is no bus protection at Coleridge or Otira, so bus faults remove all connected circuits from service. This includes the Coleridge Castle Hill Arthur s Pass Otira circuit, causing a loss of supply at Castle Hill and Arthur s Pass. The customers (Buller Networks, Westpower, Network Tasman, or Orion) have not requested a higher security level. If increased bus security is required, the options typically include bus reconfiguration and/or additional bus circuit breakers. Future investment will be customer driven. 282

14 West Coast voltage quality and transmission capacity This issue is for information only The West Coast load is mainly supplied from the National Grid via two Inangahua Kikiwa circuits, with lower capacity backup circuits from Coleridge. There are single bus sections at Kikiwa and at Inangahua, so a bus outage will disconnect both circuits. This will cause: low voltage issues at all and buses, and transmission circuit capacity issues in the West Coast region. The effect of the low voltages and circuit overloading is difficult to predict. The outcome is heavily influenced by the local generation and load composition at the time of the outage. The low voltages may cause enough motor load to trip so the transmission system stays intact and continues to supply the remaining load. Otherwise, one or more circuits will trip, causing a total loss of supply to some or all of the grid exit points in the region. In addition, an outage of the Kikiwa 220 kv bus, which disconnects the Kikiwa T2 interconnecting transformer, will cause the transmission bus voltages in the region to fall below 0.90 pu towards the end of the forecast period. The customers (Westpower, Buller Networks, Network Tasman, and Orion) have not requested a higher security level and there are no plans to increase bus security. Replacing the Kikiwa T1 interconnecting transformer with a higher rated unit (see Sections and ) will address the issue of a Kikiwa 220 kv bus outage Other regional items of interest There are no other items of interest identified to date beyond those in Section 16.8 and 8.9. See Section 8.11 for information about generation scenarios, proposals and opportunities relevant to this region West Coast generation scenarios, proposals and opportunities This section details relevant regional issues for selected generation scenarios, generation proposals under investigation by developers and in the public domain, or other generation opportunities. The impact of committed generation projects on the grid backbone is dealt with separately in Chapter 6. The maximum generation that can be connected depends on several factors and usually falls within a range. Generation developers should consult with us at an early stage of their investigations to discuss connection issues Impact of generation scenarios on regional plan The generation scenarios (see Chapter 5) represent a series of possible future generation outcomes. This section presents only those scenarios relevant to this region for the next 15 years. All generation scenarios except scenario 3 anticipate some new generation connections in the West Coast region. 283

15 At Dobson, generation may connect to the or 33 kv bus. If generation is connected to the 33 kv bus, generation may be constrained by the 66/33 kv supply transformer capacity under light load conditions and for supply transformer outages. Generation scenario 2 anticipates a total of 115 MW generation connections onto the Inangahua Waimangaroa Robertson Street Westport spur. Section discusses the impacts and the likely system developments to relieve the constraints Maximum regional generation Maximum generation estimates assume a South Island light load profile and that the generation in the West Coast region is high (with Kumara generating 10 MW). For generation connected at the Kikiwa 220 kv bus, the maximum generation that can be injected under n-1 is approximately 800 MW. The constraint is the Islington Kikiwa 2 or 3 circuit when either one of the two circuits is out of service. For a West Coast load of 35 MW, the estimated maximum generation injection 150 at the two key busses is as follows: At the Kikiwa bus, under normal operating conditions, the maximum is 260 MW to avoid overloading the Kikiwa T2 interconnecting transformer. The generation injection value decreases to approximately 135 MW for an outage of Kikiwa T2 to avoid overloading the Kikiwa Stoke circuits At the Inangahua bus under normal operating conditions, the maximum is approximately 165 MW to avoid overloading the Inangahua Murchison Kikiwa 1 circuit. The generation injection value decreases to approximately 95 MW for an outage of the Inangahua Murchison Kikiwa 2 circuit to avoid overloading the Kikiwa Stoke circuit. Generation connected to the West Coast transmission network may be constrained by several low capacity circuits Generation connected to the Inangahua to Westport spur Two circuits form the Inangahua to Westport spur, with substations at Waimangaroa, Robertson Street and Westport. The Inangahua Waimangaroa 1 circuit is rated at 101/111 MVA (summer/winter) and the Inangahua Waimangaroa 2 circuit is rated at 56/68 (summer/winter). Depending on the amount of generation connected to the spur, it may be necessary to: close the split at the Waimangaroa bus install a special protection scheme to allow unconstrained generation injection, and/or increase the circuit capacity between Waimangaroa, Inangahua, and Kikiwa. Generation connected to the spur also forms part of the maximum level of generation that can be connected within the region (see Section ). 150 The generation injection at a bus applies if the generation is connected directly at the bus, or indirectly at other locations within the region. For example, generation at Dobson or along the Waimangaroa spur connects indirectly to the Inangahua bus and Kikiwa bus. Generation connected to the system in the Nelson Marlborough region (Chapter 15) also injects indirectly to the Kikiwa bus. 284